Electronic amplifier can mean thus a kind of electronic circuit or stage of this, as a modular computer that performs the same function, and that is usually part of HIFI equipment. Its function is to increase the intensity of current, voltage or power signal is applied to its input, yielding the increased signal at the output. To amplify the power necessary to obtain energy from external power supply. In this sense, the amplifier can be considered as a modulator output power
HIFI Class D amplifier circuit of 200W RMS into 4 Ohm speaker.
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The amplifier can perform its function in a passive manner by varying the ratio between current and voltage at constant power (similar to a transformer), or actively, taking power from a power supply and increasing the power of the signal leaving the amplifier, usually keeping the shape of the signal, but giving it more widely.
The relationship between input and output of the amplifier can be expressed in terms frequency of the input signal, which is called transfer function, which indicates the gain of the same for each frequency. It is customary to keep an amplifier working within a certain range of frequencies over which behaves linearly, which means that its gain is constant for any amplitude to its input.
The main component of these amplifiers, called active element may be a vacuum tube or transistor. The vacuum tubes are often used even in some audio amplifiers designed specifically for the frequency response of these, preferred in some styles. Represent the base transistors electronics modern. They are designed with more complex circuits such as operational amplifiers, which in turn are used in others such as instrumentation amplifiers.
amplifier classes
consuming high continuous flow of power regardless of the existence of signal in the input. This amplification has the disadvantage of generating a strong and constant amount of heat that must be dissipated. This causes a very low yield, to miss an important part energy that goes into it. It is common in audio circuits and high-end home computers, as they provide great sound quality, being very linear, with little distortion.
has a bias current greater than the maximum output current can be delivered. Class A amplifiers often consist of an output transistor connected to the positive terminal of the power supply and a constant current transistor connected from output to negative power supply. When no input signal constant bias current flows directly from positive to negative to negative power supply, power consumed not useful.
Class B
Class B.
Class B amplifiers are characterized by almost zero intensity through their transistors when no input signal circuit. This is what polarizes the transistors to fit in driving area, so consumption is lower than in class A, although the quality is somewhat lower because of the way in which the wave is transmitted. It is used in telephone systems, portable transmitters, security and warning systems, but not audio.
class B amps have output stages with zero bias current. Have a significant distortion with small signals, known as filter distortion, because it occurs at the point where the output stage crosses between the source and the current buffer.
Class C
Class C amplifiers are similar to class B in the output stage has zero bias current. However, they have a region of zero idle current which is over 50% of total supply voltage. The disadvantages of class B amplifiers are more evident in Class C amplifiers This type of amplifier used in audio.
Class AB Class AB amplifiers are a small constant power at its input, independent of the existence of signal. It is the most common audio at high yield and quality. These amplifiers are named because with large signals behave as a class B, but with small signals behave as a class A.
have two output transistors, such as class B, but unlike them, have a small free stream flowing between the terminals of the power supply, yet not so high as in Class A. This free flow corrects almost all of the nonlinearities associated with the distortion of the filters.
Class D amplifiers have high energy efficiency, superior in some cases 95%, reducing the size of heat sinks needed, and therefore the overall size and weight of the circuit.
Although previously limited to portable devices or subwoofers, in which distortion or bandwidth, are not determinants with modern technology there are class D amplifiers for the entire frequency band, with distortion levels similar to class AB.
Class D amplifiers are based on switching between two states, which output devices are always on the cutting areas or saturation, cases in which the power dissipated in them is practically nil, except at the transition, the duration must be minimized to maximize performance.
The switching signal can be generated in various ways, but the most common is the pulse width modulation. Then it must be filtered to recover the signal information, for which the switching frequency must be greater than the bandwidth of the signal at least 10 times.
Class D amplifiers require careful design to minimize electromagnetic radiation they emit, and thus avoid interfering with nearby equipment, typically in the FM band.
Other classes
Classes E, G and H are not standardized as A and B. These variations of the classic circuits, which depend on the variation of supply voltage to minimize power dissipation in the power transistors in each time, depending on the input signal.
Mario Dominguez Zambrano
EES Section: 02
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